The conventional packaging for semiconductor industries is to dispose a chip on a substrate, then wire bond the chip to the substrate to complete electrical connections between the two. Flip chip bonding is a more advanced packaging technology which is different from the conventional packaging method where bumps such as solder bumps or solder balls are disposed on the active surface of a chip in wafer form then the bumped chip is flipped with the active surface facing toward the substrate where the bumps become the electrical connections between the chip and the substrate to reduce the electrical path between the chip and the substrate to achieve a better electrical performance than wire bonding.
Then, IBM was the first to develop an innovated flip-chip technology where metal pillars are implemented to replace the conventional solder balls. Solder bonding materials are implemented to joint the metal pillars of a chip to the bonding pads of a substrate so that the metal pillars don't change their shapes as the conventional solder balls during reflow, therefore, the pitches between metal pillars can further be reduced below 50 um such as 30 um to achieve higher density of bump layout. In some package products, RDL (redistribution layer) on chip can be eliminated. This technology is called MPS-C2 (Metal Post Solder-Chip Connection), the related package structure is disclosed in U.S. Pat. No. 6,229,220 B1 titling “Bump Structure, Bump Forming Method and Package Connecting Body”.
As shown in FIG. 1, a conventional MPS-C2 flip chip package 100 primarily comprises a chip 110 and a substrate 120. A plurality of bumps 112 such as metal pillars disposed on the active surface 111 of the chip 110 for flip-chip bonding the chip 110 to the substrate 120. The substrate 120 has a plurality of bonding pads 121 corresponding to the bumps 112. To describe in depth, the bumps 112 are bonded to the bonding pads 121 by a plurality of solder bonding materials 130 to achieve electrical connection between the chip 110 and the substrate 120. Furthermore, the flip chip package 100 further comprises an encapsulant 140 to encapsulate the bumps 112, the bonding pads 121, and the solder bonding materials 130.
Generally speaking, bumps serve as the electrical connections for fine-pitch high-density applications such as the conventional flip-chip technology including the MPS-C2 technology. Therefore, during flip-chip bonding processes, the recognition system of a flip-chip die bonder searches for two-dimensional alignment marks on a substrate for accurate alignment where high accurate alignment system is needed such as alignment tolerance under 25 um to achieve flip-chip bonding the chip 110 to the substrate 120. However, a flip-chip die bonder with high accuracy is very expensive. Moreover, even after flip-chip bonding the chip 110 to the substrate 120 with good alignment, but the following processes such as transportation of reflow processes, the vibration of the equipment, and the flooding of solder bonding materials or fluxes are easily causing the bumps 112 bonded to wrong bonding pads 121 leading to electrical failure. It is even worst for MPS-C2 technology with the drop of productivity.